Chytrid fungus distribution in Nebraska

Duration

August 2010 - May 2014

Narrative

Many worldwide amphibian population declines and mass mortality events have been attributed a fungal infection chytridiomycosis (chytrid) caused by the fungal zoospore Batrachochytrium dendrobatidis (Bd). Although the exact mechanism by which mass mortalities occur from chytrid is unknown, it is hypothesized that the chytrid fungus infects keratinized epidermal cells of postmetamorphic frogs with death caused by: 1) disruption of osmoregulation; 2) the absorption of a fungal toxin; 3) or a combination of these factors. Concern over the potential ecological consequences of such rapid and drastic extinctions has led to an increase in effort studying the potential effects of emerging infectious disease on amphibian populations. Furthermore, scientific and technological advances in non-invasive techniques to detect the chytrid fungus have changed the ability of researchers and managers to track the distribution of and measure the population fluctuations and declines caused by infectious disease such as chytrid.

The chytrid fungus is known to occur in Nebraska and has been found in amphibian populations located in eastern Nebraska as well as along the Central Platte River. Although sporadic testing for the chytrid fungus in populations of native amphibians has occurred in Nebraska, a statewide survey has never been conducted. This lack of knowledge pertaining to the current distribution of chytrid the state must be rectified. Doing so will not only allow researchers to know where chytrid is currently found in the state, but also aid in the development of predictive models and help in the understanding of factors that may help or mitigate the further spread of chytrid.

The primary goal of this study to determine the current extent of chytrid in Nebraska by swabbing larval amphibian populations statewide. Using PCR, the samples will be tested for the presence of Bd zoospores. The presence/absence of chytrid in amphibian populations will be used to model the distribution of chytrid based on environmental covariates associated with wetland condition and amphibian call surveys. The results of these models will be used to develop predictive maps of the potential spread of chytrid based on important environmental and anthropogenic variables.

During the spring and summer of 2011 and 2012, researchers visited wetlands in eastern and central Nebraska. During site visits, tadpoles were captured using dip nets. At those sites where tadpoles were captured, each individual was swabbed using a sterile swab. In 2011 and 2012, 168 swabs were collected from 5 frog species at 21 sites. Preliminary PCR results detected chytrid in 62% of the sites. Additionally, chytrid was detected in at least one swab from each species. The detection rate (d) was highest in bullfrogs (n = 9; d = 1.00) and lowest in plains leopard frogs (n = 78; d = 0.10). The detection rate did not appear to vary between months (May – n= 56, d = 0.125; June – n = 112 d = 0.17). An additional 10 samples were collected during 2013. Sampling will continue during the spring and early summer of 2014.